The pilot of a SilkAir plane that went down in Indonesia in 1997, killing 104 people, probably crashed the jet on purpose, United States investigators have said.

They say the cockpit voicebox recorder appeared to have been intentionally disconnected and the pilot, Tsu Way Ming, did not attempt to reverse the plane's nosedive.

The accident can be explained by intentional pilot action

US investigators

Speculation that Mr Tsu had committed suicide taking his passengers with him has circulated ever since the crash, but has not been officially voiced in public until now.

The US findings contradict an Indonesian investigation's final report on the crash this week, which rejected the suicide theory.

The Singapore bound Boeing 737-300 crashed into a jungle river in Palembang on 19 December 1997, shortly after leaving the Indonesian capital Jakarta.

In a letter to Indonesian investigators this week, the US National Transportation Safety Board (NTSB) said there was nothing wrong with the plane and "the accident can be explained by intentional pilot action".

The NTSB said investigations showed Mr Tsu, once a stunt flyer with the Singapore Air Force, was in serious debt from financial market speculation and had been reprimanded by management several times in the weeks before the crash.

Voice recorder

On Thursday, Indonesian investigators said they could not establish the cause of the crash "due to the highly fragmented wreckage and the nearly total lack of useful data, information and evidence".

But Singapore police and Indonesia's National Transportation Safety Committee both issued statements saying there was no evidence to show Mr Tsu had suicidal tendencies.

Singapore officials said they accepted the Indonesian report's findings - SilkAir is a subsidiary of Singapore Airlines.

However, the NTSB said in its letter that the evidence "suggests that the cockpit voice recorder was intentionally disconnected".

It added that the pilot could have reversed the plane's nosedive but that this was "not attempted".

Nose-down

A separate report from the US board argued that the plane could not have done what it did without deliberate action from the pilot.

It said the wreckage showed the plane's engines were set to high power and that controls were set to a "nose-down" position.

The US board said it was disappointed the Indonesian report failed to analyse information about the pilot's financial debts.

The US was asked to participate in the investigation because the plane was made by Seattle-based Boeing Co.

Relatives of some of the victims have filed legal actions against Boeing. A number of families have also filed claims against SilkAir.